1. The problem statement, all variables and given/known data What is the definition of the phase (not phase shift) at some time t of a wave? Specifically, for a wave oscillating according to the equation [tex]x=A\sin(\omega t + \phi),[/tex] what is the the phase at some time [tex]t[/tex]? 2. Relevant equations 3. The attempt at a solution Our book says the phase is [tex]\omega t + \phi,[/tex] while http://en.wikipedia.org/wiki/Phase_(waves)" says that it can also be [tex]\omega t + \phi[/tex] modulo [tex]2\pi[/tex]. Which is right?